---
title: CanvasRenderingContext2D.globalCompositeOperation
slug: Web/API/CanvasRenderingContext2D/globalCompositeOperation
tags:
  - Canvas
  - CanvasRenderingContext2D
translation_of: Web/API/CanvasRenderingContext2D/globalCompositeOperation
---
<div>{{APIRef}}</div>

<p>Canvas 2D API的 <code><strong>CanvasRenderingContext2D</strong></code><strong><code>.globalCompositeOperation</code></strong>  属性设置要在绘制新形状时应用的合成操作的类型，其中type是用于标识要使用的合成或混合模式操作的字符串。</p>

<p>在 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial">Canvas Tutorial</a> 中查看 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial/Compositing">Compositing</a> 章节。</p>

<h2 id="语法">语法</h2>

<pre class="syntaxbox"><var><em>ctx</em>.globalCompositeOperation = type;</var></pre>

<h3 id="类型">类型</h3>

<p>{{EmbedLiveSample("合成示例", 750, 6750, "" ,"Web/API/Canvas_API/Tutorial/Compositing/Example")}}</p>

<h2 id="示例">示例</h2>

<h3 id="Using_the_globalAlpha_property" name="Using_the_globalAlpha_property">使用 <code>globalCompositeOperation</code> 属性</h3>

<p>这是一段使用 <code>globalCompositeOperation</code> 属性的简单的代码片段，绘制了2个矩形在重叠时相互排斥的情况。</p>

<h4 id="HTML">HTML</h4>

<pre class="brush: html">&lt;canvas id="canvas"&gt;&lt;/canvas&gt;
</pre>

<h4 id="JavaScript">JavaScript</h4>

<pre class="brush: js; highlight[4]">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.globalCompositeOperation = "xor";

ctx.fillStyle = "blue";
ctx.fillRect(10, 10, 100, 100);

ctx.fillStyle = "red";
ctx.fillRect(50, 50, 100, 100);
</pre>

<p>修改下面的代码并在线查看 canvas 的变化：</p>

<div class="hidden">
<h6 id="Playable_code" name="Playable_code">Playable code</h6>

<pre class="brush: html">&lt;canvas id="canvas" width="400" height="200" class="playable-canvas"&gt;&lt;/canvas&gt;
&lt;div class="playable-buttons"&gt;
  &lt;input id="edit" type="button" value="Edit" /&gt;
  &lt;input id="reset" type="button" value="Reset" /&gt;
&lt;/div&gt;
&lt;textarea id="code" class="playable-code" style="height:120px;"&gt;
ctx.globalCompositeOperation = "xor";

ctx.fillStyle = "blue";
ctx.fillRect(10, 10, 100, 100);

ctx.fillStyle = "red";
ctx.fillRect(50, 50, 100, 100);&lt;/textarea&gt;
</pre>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);
</pre>
</div>

<p>{{ EmbedLiveSample('Playable_code', 700, 380) }}</p>

<h2 id="规范描述">规范描述</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('HTML WHATWG', "scripting.html#dom-context-2d-globalcompositeoperation", "CanvasRenderingContext2D.globalCompositeOperation")}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('Compositing')}}</td>
   <td>{{Spec2('Compositing')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<p>{{Compat("api.CanvasRenderingContext2D.globalCompositeOperation")}}</p>

<h3 id="WebKitBlink-specific_注解">WebKit/Blink-specific 注解</h3>

<ul>
 <li>在基于 WebKit- 和 Blink- 的浏览器中，除了此属性外，还实现了一个不标准的并且不赞成使用的方法 <code>ctx.setCompositeOperation()</code>。</li>
</ul>

<h3 id="Gecko-specific_注解">Gecko-specific 注解</h3>

<ul>
 <li>早起的规范草案指定了 "darker"值。 然而， Firefox 在第4个版本({{bug(571532)}})移除了对 "darker"的支持。参见 <a href="http://dropshado.ws/post/77229081704/firefox-doesnt-support-canvas-composite-darker">这篇文章</a> 建议如何使用不同的值实现和"darker"类似的效果。</li>
</ul>

<h2 id="参见">参见</h2>

<ul>
 <li>接口定义，{{domxref("CanvasRenderingContext2D")}}</li>
 <li>{{domxref("CanvasRenderingContext2D.globalAlpha")}}</li>
</ul>